<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    
</body>
</html>

<script>


// @testable
class MyTestableClass {
  // ...
}

// function testable(target) {
//   target.isTestable = true;
// }

 // true
// console.log(MyTestableClass.isTestable)
</script>